Automatic power transmissions used in modern vehicles typically utilize a multi-function turbomachine or device commonly referred to as a hydrodynamic torque converter. A hydrodynamic torque converter is used to automatically disengage a rotating engine crankshaft from a transmission input shaft during vehicle idling conditions to enable the vehicle to stop and/or to shift gears without stalling. Additionally, the torque converter is used as a torque multiplier for multiplying engine torque in the lower vehicle speed range until the vehicle speed nearly matches the engine speed.
Within a torque converter, a number of specially constructed internal components combine to enable an efficient fluid coupling effect between the disparately rotating engine and transmission shafts. In particular, a standard or conventional torque converter consists of an engine-driven pump or impeller, which is the driving member of the torque converter giving impetus to a stream of hydraulic fluid. The pump is connected to the engine crankshaft and therefore rotates in unison with the engine, thereby accelerating a supply of hydraulic fluid and directing the accelerated fluid to the second component, the turbine. The turbine, which is driven by the accelerated fluid discharged by the pump, is typically splined to a transmission input shaft and converts the fluid energy imparted by the fluid stream into useable mechanical energy, which is transmitted to the splined transmission input shaft to propel the vehicle. Finally, a stationary member or stator is included within the torque converter for redirecting the fluid stream between the pump and turbine. The stator is connected to a fixed reaction shaft through a one-way clutch that allows the stator to free-wheel when torque multiplication is no longer possible.
Torque converters are designed to slip at lower vehicle speeds in order to enable the transmission to rotate at a slower rate than the coupled engine, with the slip rate gradually diminishing as the vehicle is accelerated. Effectively, the torque converter holds the engine speed nearly constant, allowing the transmission speed to gradually reach or approach the engine speed as the vehicle accelerates. The torque converter input speed, identical with the engine speed and stated in revolutions per minute, is an important design factor that is substantially affected by the outlet angle of the stator. The outlet angle is primarily determined by the configuration or construction of a plurality of stator blades within the stator. However, the torque converter input speed depends in large part on the engine output torque, and therefore a more descriptive variable, the “K-factor”, is usually used to rate or describe an individual torque converter. K-factor refers to the input speed divided by the square root of the engine torque, as measured at any torque converter operating point. The operating point of a torque converter is most conveniently defined by the ratio of the output speed to the input speed of the torque converter. This parameter or variable is known as the torque converter speed ratio.
Vehicle fuel economy and performance is enhanced when the operating or performance characteristics of a given torque converter are automatically optimized. While a variable-blade angle stator may be used, wherein individual piston-actuated stator blades are allowed to pivot on shafts running from shell to core in order to adjust the stator blade position and angle, such variable designs tend to be intricate and therefore may be less than optimal due in part to their relative cost and complexity.